Name
SGIS_sharpen_texture
Name Strings
GL_SGIS_sharpen_texture
Version
$Date: 1995/07/09 06:48:51 $ $Revision: 1.16 $
Number
22
Dependencies
EXT_texture is required
EXT_texture3D affects the definition of this extension
EXT_texture_object affects the definition of this extension
Overview
This extension introduces texture magnification filters that sharpen
the resulting image by extrapolating from the level 1 image to the
level 0 image. Sharpening can be enabled for all color channels, for
the alpha channel only, or for the red, green, and blue channels only.
New Procedures and Functions
void SharpenTexFuncSGIS(enum target,
sizei n,
const float* points);
void GetSharpenTexFuncSGIS(enum target,
float* points);
New Tokens
Accepted by the parameter of TexParameteri and TexParameterf,
and by the parameter of TexParameteriv and TexParameterfv, when
their parameter is TEXTURE_MAG_FILTER:
LINEAR_SHARPEN_SGIS
LINEAR_SHARPEN_ALPHA_SGIS
LINEAR_SHARPEN_COLOR_SGIS
Accepted by the parameter of GetTexParameteriv and
GetTexParameterfv:
SHARPEN_TEXTURE_FUNC_POINTS_SGIS
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
GL Specification Table 3.7 is updated as follows:
Name Type Legal Values
---- ---- ------------
TEXTURE_WRAP_S integer CLAMP, REPEAT
TEXTURE_WRAP_T integer CLAMP, REPEAT
TEXTURE_WRAP_R_EXT integer CLAMP, REPEAT
TEXTURE_MIN_FILTER integer NEAREST, LINEAR,
NEAREST_MIPMAP_NEAREST,
NEAREST_MIPMAP_LINEAR,
LINEAR_MIPMAP_NEAREST,
LINEAR_MIPMAP_LINEAR,
FILTER4_SGIS
TEXTURE_MAG_FILTER integer NEAREST, LINEAR,
FILTER4_SGIS,
LINEAR_DETAIL_SGIS,
LINEAR_DETAIL_ALPHA_SGIS,
LINEAR_DETAIL_COLOR_SGIS,
LINEAR_SHARPEN_SGIS,
LINEAR_SHARPEN_ALPHA_SGIS,
LINEAR_SHARPEN_COLOR_SGIS
TEXTURE_BORDER_COLOR 4 floats any 4 values in [0,1]
DETAIL_TEXTURE_LEVEL_SGIS integer any non-negative integer
DETAIL_TEXTURE_MODE_SGIS integer ADD, MODULATE
Table 3.7: Texture parameters and their values.
3.8.2.2 Texture magnification with sharpening
Three additional texture magnification filters are defined for texture
magnification. These values, which are assigned to TEXTURE_MAG_FILTER,
are LINEAR_SHARPEN_SGIS, LINEAR_SHARPEN_ALPHA_SGIS, and
LINEAR_SHARPEN_COLOR_SGIS. All three filters sample the level 0
texture array exactly as it would be sampled with filter mode LINEAR.
If texture levels 0 and 1 are "complete", as described in the Mipmapping
portion of Section 3.8.1 (Texture Minification) of the GL Specification,
the level 1 array of the texture is also linearly sampled, just as though
mipmap minification was being performed with LOD (the level of detail
parameter) valued near 1.0. If levels 0 and 1 are not complete, it is
as though the magnification texture filter was LINEAR. (Although
querying the magnification filter value will return the value as
specified.)
The texture value computed from the level 0 array (T0) and the
value computed from the level one array (T1) are combined to compute
the final texture value (T):
T' = ((1 + F(LOD)) * T0) - (F(LOD) * T1)
/ 0 T' < 0
T = < T' 0 <= T' <= 1
\ 1 T' > 1
F is a function of the level-of-detail parameter LOD, which is
represented by the Greek character lambda in the GL Specification.
The function F of level-of-detail parameter LOD is specified by
calling SharpenTexFuncSGIS with set to TEXTURE_1D, TEXTURE_2D,
or TEXTURE_3D_EXT, pointing at an array of pairs of floating
point values, and set to the number of value pairs in . The
first value of each value pair in specifies a value of LOD, and
the second value of each value pair specifies the corresponding function
value. The order in which the points are specified is not significant.
The value pairs in completely specify the function,
replacing any previous specification that may have existed. Since
negative values of LOD correspond to magnification and positive values
correspond to minification, the points should have negative values for
LOD (though it is not an error to specify positive values).
Function F is evaluated by sorting the value pairs specified by
SharpenTexFuncSGIS by LOD value, then fitting a curve through these
points. This curve may be linear between adjacent points, or it may be
smoothed, but it will pass exactly through the points, limited only by
the resolution of the implementation. The value pair with the lowest
LOD value specifies the function value F for all values of LOD less than
or equal to that pair's LOD. Likewise, the value pair with the greatest
LOD value specifies the function value F for all values of LOD greater
than or equal to that pair's LOD. F is undefined if two or more value
pairs have the same LOD value.
If the texture magnification filter is LINEAR_SHARPEN_SGIS, then both
the color and the alpha components of T are computed as described
in the equations above. If the filter is LINEAR_SHARPEN_COLOR_SGIS,
then all components of T other than alpha are computed as described
above, and the alpha component of T is computed as if the texture
magnification filter were LINEAR. Finally, if the filter is
LINEAR_SHARPEN_ALPHA_SGIS, the alpha component of T is computed as
described in the equations above, and all other components of T
are computed as if the texture magnification filter were LINEAR.
Minification vs. Magnification
------------------------------
If the magnification filter is given by LINEAR_SHARPEN_SGIS,
LINEAR_SHARPEN_ALPHA_SGIS, or LINEAR_SHARPEN_COLOR_SGIS, and the
minification filter is given by NEAREST_MIPMAP_NEAREST or
LINEAR_MIPMAP_NEAREST, then c = 0.5. The parameter c is used to
determine whether minification or magnification filtering is done,
as described in Section 3.8.2 of the GL Specification (Texture
Magnification).
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Framebuffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
GetSharpenTexFuncSGIS is not included in display lists.
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
The number of points in the sharpen texture function specification of
a texture is queried by calling GetTexParameteriv or GetTexParameterfv
with set to the target of the desired texture and set
to SHARPEN_TEXTURE_FUNC_POINTS_SGIS. The function
GetSharpenTexFuncSGIS returns in all of the points in the
sharpen texture function of texture .
Additions to the GLX Specification
None
GLX Protocol
Two new GLX protocol commands are added.
SharpenTexFuncSGIS
2 12+4*2*n rendering command length
2 2052 rendering command opcode
4 ENUM target
4 INT32 n
4*2*n LISTofFLOAT points
GetSharpenTexFuncSGIS
1 CARD8 opcode (X assigned)
1 17 GLX opcode (glXVendorPrivateWithReply)
2 4 request length
4 4097 vendor specific opcode
4 GLX_CONTEXT_TAG context tag
4 ENUM target
=>
1 1 reply
1 unused
2 CARD16 sequence number
4 n reply length, m = n
4 unused
4 CARD32 n
16 unused
n*4 LISTofFLOAT32 points
Note that n may be zero, indicating that a GL error occurred.
Other n must be even and n >= 2.
Dependencies on EXT_texture
EXT_texture is required.
Dependencies on EXT_texture3D
If EXT_texture3D is not implemented, references in this specification
to TEXTURE_3D_EXT are invalid, and should be ignored.
Dependencies on EXT_texture_object
If EXT_texture_object is implemented, the state values named
SHARPEN_TEXTURE_FUNC_POINTS_SGIS
are added to the state vector of each texture object. When an attribute
set that includes texture information is popped, the bindings and
enables are first restored to their pushed values, then the bound
textures have their sharpen parameters restored to their pushed values.
Errors
INVALID_ENUM is generated if SharpenTexFuncSGIS or
GetSharpenTexFuncSGIS parameter is not TEXTURE_1D, TEXTURE_2D,
or TEXTURE_3D_EXT.
INVALID_VALUE is generated if SharpenTexFuncSGIS parameter is
negative.
INVALID_OPERATION is generated if SharpenTexFuncSGIS or
GetSharpenTexFuncSGIS is executed between execution of Begin and the
corresponding execution to End.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
SHARPEN_TEXTURE_FUNC_POINTS_SGIS GetTexParameteriv n x Z+ 2 texture
GetSharpenTexFuncSGIS n x m x R {0, 0}, {-4, 1} texture
New Implementation Dependent State
None